before_install steps don't merge
before_install steps don't merge

Moved the validation of before_install into install.

sdiehl/ghc,snowleopard/hadrian,quchen/shaking-up-ghc,snowleopard/shaking-up-ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,izgzhen/hadrian,sdiehl/ghc,bgamari/shaking-up-ghc,sdiehl/ghc,sdiehl/ghc